1. Field of the Invention
This invention relates to the recovery of starch from cereal grains such as corn, wheat, rice, milo, and the like and, more particularly, to the recovery of starch from cereal grains in the form of an aqueous slurry.
2. Description of the Prior Art
With the ever-increasing depletion of economically recoverable petroleum reserves, the production of ethanol from vegetative sources as a partial or complete replacement for conventional fossil-based liquid fuels becomes more attractive. In some areas, the economic and technical feasibility of using a 90% unleaded gasoline--10% anhydrous ethanol blend ("gasohol") has shown encouraging results. According to a recent study, gasohol powered automobiles have averaged a 5% reduction in fuel compared to unleaded gasoline powered vehicles and have emitted one-third less carbon monoxide than the latter. In addition to offering promise as a practical and efficient fuel, biomass-derived ethanol in large quantities and at a competitive price has the potential in some areas for replacing certain petroleum-based chemical feedstocks. Thus, for example, ethanol can be catalytically dehydrated to ethylene, one of the most important of all chemical raw materials both in terms of quantity and versatility.
The various operations in processes for obtaining ethanol from such recurring sources as cellulose, cane sugar, amylaceous grains and tubers, e.g., the separation of starch granules from non-carbohydrate plant matter and other extraneous substances, the chemical and/or enzymatic hydrolysis of starch to fermentable sugar (liquefaction and saccharification), the fermentation of sugar to a dilute solution of ethanol ("beer") and the recovery of anhydrous ethanol by distillation, have been modified in numerous ways to achieve improvements in product yield, production rates and so forth (see, for example, U.S. Pat. No. 3,236,740 and the booklet "Industrial Alcohol by Continuous Fermentation and Vacuum Distillation With Low Energy Consumption", of Chemapec, Inc., Woodbury, N.Y. For ethanol to realize its vast potential as a partial or total substitute for petroleum fuels or as a substitute chemical feedstock, it is necessary that the manufacturing process be as efficient in the use of energy and raw materials as possible so as to maximize the energy return for the amount of ethanol produced and enhance the standing of the ethanol as an economically viable replacement for petroleum based raw materials. To date, however, relatively little concern has been given to the energy and raw material requirements for manufacturing ethanol from biomass and consequently, little effort has been made to minimize the thermal expenditure and waste incurred in carrying out any of the aforesaid discrete operations involved in the manufacture of ethanol from vegetative sources.
It is common practice to recover starch from corn in a sequence of operations featuring removal of germ from steeped corn, removal of fiber from the degerminated corn, separation of the corn starch from the gluten and washing and drying of the corn starch to provide a food grade material suitable for use per se or for conversion to sugar (see, for example, the booklet "Corn Wet Milling Processes and Equipment From Dorr-Oliver", of Dorr-Oliver Incorporated, Stamford, Conn.). Under the process conditions of this and similar starch recovery procedures, soluble carbohydrates and proteins present in the grain are discarded or otherwise separated from the starch. While this loss of soluble carbohydrates and proteins is not considered a problem in the starch and sugar industries where the purity and quality of the end product is of paramount importance, it represents a substantial disadvantage to the full and efficient utilization of grain starch as a raw material for the production of inexpensive industrial ethanol. The loss of soluble carbohydrate which represents a significant portion of the total quantity of carbohydrate present in cereal grains accounts for a substantial diminution of raw material which would be useful for ultimate conversion to ethanol. Similarly, the loss of soluble protein which would otherwise be available to satisfy the nutritive requirements of yeast employed in the conversion of fermentable sugar obtained by hydrolysis of the starch further militates against the use of current procedures for the recovery of starch from cereal grains.
Accordingly, there has heretofore existed a need for a process for recovering starch from cereal grains which does not result in the removal of substantial quantities of water soluble carbohydrate and/or protein therefrom.